Grinding wheel



GRINDING WHEEL Filed Dec. 24, 1940 Patented Apr. 15, 1941 2,238,351GRINDING WHEEL Edward Van der Pyl, Holden, Masa, assignor to NortonCompany, Worcester, Mass., a corporation of Massachusetts ApplicationDecember 24, 1940, Serial No. 371,543

8 Claims.

The invention relates to metal bonded'abra sives, particularly todiamond grinding wheels, and with regard to its more specific features,to a cutting-oil wheel with a metal bonded abrasive rim and a metalcenter.

One object of the invention is to provide a combination metal bond forabrasives, particularly diamonds, adapted to be soldered to a metalcenter, particularly a steel center, giving a strong union. Anotherobject of the invention is to provide a metal bond composition which'isstrongafzd also friable. Another object of the invention is to provide ametal bond composition which is heat resistant. Another object of theinvention is to. provide a metal bond composition which will holddiamondabrasive very tenaciously. Another object of the invention is toprovide a metal bond which is cold moldable and has one or more of otherdesired characteristics, such as an afiini-ty for diamonds, resistanceto heat, and friableness. Other objects will be in part obvious or inpart pointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, arrangements of parts, and in the severalsteps and relation and order of each of said steps to one or more of theothers thereof, all as will be illustratively described herein, and thescope of portion i3 which has a blunt'ta'per. As shown in Figure 2,notches M may be provided in the edge of the peripheral portion i3. Ontothe periphery i3 I mold an abrasive mixture consisting of diamondabrasive i5 bonded with metal bond i6 forming an abrasive portion H. Itake crushed, cleaned'and graded'dlamonds, for example of the order of46 grit size and finer, preferably as fine as 100 grit size, and to theextent of preferably between 6.25% and 60% by volume, and mix them withmetal powders'which are preferably very fine. While coarse particles maybe used, I preier electrolytic metal which is virtually an impalpablepowder. Powders in the form of metal particles the same size as theabrasive are, however, quite practical.

I make a thorough mixture of the various metal powders and thediamondsand then by the use of a mold andw-ith high pressure, mold the, mixturearound the outside of the steel center E0. The mold and the procedureused may be that disclosed in my prior copending application Serial No.295,939 filed September 21, 1939. After molding with pressure, theentire article can be readily handled and it is then placed in asintering furnace.

Considering now the particular metals'to be used, I prefer one part ofiron, one part nickel, one part tin, and one part copper. All parts aregiven by weight.

particles than 20% by weight of a cold moldable metal sethe mixturesatisfactorily to a-steel center, such lected from the group'consistingof copper and nickel. Copper is the best cold moldable metal known to mesince pure copper is quite ductile. Some other metals which are equallyductile are excluded for other reasons. For example, lead has too lowamelting point. Copper melts at 1083 C. Nickel is fairly ductile andmelts at 1452 C. Copper ispreferred to nickel and in my metal bond Ifind there should be not less than 4% by weight of copper based on thetotal bond.

Another feature of the invention is that not less than 2%. of the totalmetal bond should have a high melting point and be selected from thegroup consisting of iron and nickel. Iron has a melting point of 1530 C.By selecting a combination of metals including some with a high meltingpoint, I am enabled to braze or solder as the steel center i0, withoutchanging the character of the bond. I find it is important to have someiron in the combination and my bond, therefore, has not less than 1% ofiron based on the total metal by weight. I believe the iron gives thebond an affinity for the diamonds which increases the strength of thefinal article. with regard to the nickel, it will be seen that there aretwo reasons for using nickel-because it has a high melting point andalso because it is cold moldable. Nevertheless since the copper providesthe cold moldability and the iron imparts high melting pointcharacteristics, the metal nickel may be omitted altogether in someembodiments of my invention. Therefore, the bond consists of copper,iron and tin, and optionally nickel. It may be remarked, however, thatthe bond now known to me best suiting the conditions I desire to obtainis the one previously mentioned consisting of equal parts of the fourmetals named.

My bond should have not less With regard to the tin, which melts at 2320., this is included for several reasons. Although it is desired to havethe combination have a. high melting point, it should not have too higha melting point. The incorporation of the tin reduces the melting pointof the entire combination. Furthermore, at the temperatures used insintering the article, viz. preferably between 600 C. and 850 C., thetin melts and wets the other metals and goes into solution in some ofthem, chiefly with the copper, and assists in uniting the entire articleinto an integral structure. But equally important, or even perhaps moreimportant, the tin imparts fria-bility to the entire bond. I use enoughtin so that there shall be at least 2% tin in excess of that which goesinto solid solution in the other three metals or inthe copper and ironif only copper, iron and tin are used.

In molding the article I prefer to use a pressure of about 50 tons tothe-square inch. I prefer to sinter it between 600 C. and 850 C., for

example at 750 C., but other temperatures can be used provided the bondis capable of being sintered in the temperature range mentioned.Although the sintering, that is to say, the heating takes place afterthe pressing operation, nevertheless I believe the amount of pressureused has a very material bearing upon how much of the tin goes intosolid solution. Under the conditions named, only asmall percentage ofthe tin will go into solution into the iron and nickel and remain as asolid solution after cooling. More will go into the copper and remain asa solid solution therein. I use a total amount of tin such that there isin the final article 2% of tin in excess of .the tin that is in solidsolution. I believe that under the conditions named, somewhere between15% and 16% of tin will stay in solid solupure metal powders under apressure of about tons to the square inch, then sintering them at atemperature of 750 C. according to the following table, in which theparts are percentages and are given by weight.

Table Order of preference Cu Sn Fe Ni B Rockwell 84 14 2 0 70 84 14 1 110 l. 66 44. 17 44. l7 10 10 1. 66 l 87. 34 30 10 i. 66 0 88. 34 23 8414 0 2 1 10 1. 66 87. 34 l 4 10 l. 66 88. 34 0 4 0 0 50 50 36 0 50 50 0Soft 0 50 0 50 Soft It is believed that so far as tin forms. a solidsolution with the other metals, the resulting product will be ductileand not friable. For'example, bronzes with a low percentage of tin areductile. I believe it is the free tin which gives friability, and thisis a very desirable product for an abrasive article since it reduces oreliminates loading.

tion in a mixture of copper and tin aloner Iron and nickel are believedto hold in solid solution only a minor amount of tin, a fraction of aper cent in each case, under the processes and at the temperaturesherein specified.

In order to determine whether or not a particular bond has thischaracteristic, it can be sliced and etched in various cross sectionsand the areas measured to determine the amount of free tin. The rest ispresumed to be in solid solution and by comparison with the amount oftin by weight introduced into the combination, it can then readily bedetermined whether the amount of tin satisfies the foregoingrequirements. The excess of tin over that in solid solution can also beascertained by well known freezing point" methods employing pyrometricobservations. Of course, in any case, the proportions of the variousmetals forming the bond are known.

Another feature of the metal bond is that the fusing point of the entirebond after sintering should notbe lower than 750 C. If it is lower thanthis, the metal bonded abrasive portion and the steel backing or centercannot so readily be soldered or brazed together.

To avoid oxidation of the diamonds, it is pre- .ence in the table.

If insufficient copperis used, the mixture of metals is difficult tomold and the final article may be found to be spalled. Such was the casewith the items marked 7 and 8 in order of prefer- Resuming thedescription of a specific embodiment of the invention, after the moldingof the article with pressure it is stripped from the mold and placed ina slntering furnace which may comprise a closed chamber with suitableheating coils and pipe connections for the introduction of hydrogentemperature control apparatus to keep the furnace at the selectedtemperature.

One or more molded articles are placed in this furnace, the hydrogen isturned on, and the furnace is gradually raised to the selectedtemperature and kept at this temperature for a period of 1 to 6 hoursafter which the articles are removed. The union between the steel centerIn and the peripheral abrasive portion Il may not be satisfactory merelyas the result of sintering. I prefer to braze or solder the partstogether and this may be done as follows:

The sintered article is slowly rotated on a vertical axis and as it isrotated the rim is heated with a blow torch. The rim is heated to atemperature sumcient to melt a wire solder which melts at 718 C. Thesolder is melted in the reentrant angle between the steel center -10 andthe abrasive. portion l1. As t'neportion I1 is heated it expands andopens a gap between it and the steel center I thus allowing the solderto flow between the parts to make a strong union. A characteristic ofthe metal bond in question is that it is readily wetted by silver solderwhich melts. at 725 C. and which may consist of silver, 20% copper, and10% zinc. This solder also readily wets the steel center l0 andforms astrong union with it.

The final article is-mechanically strong as a whole, and the bond isstrong. but yet it is friable;

that is to say, it will gradually crumble away leaving the diamondgrains well exposed for cutting. But so long as it lasts it holds thediamonds very tenaciously. It is characterized as a .various objectshereinabove set forth together with many thoroughly practical advantagesare successfully achieved. As various possible embodiments might be madeof the mechanical features ofthe above invention and as the art hereindescribed might be varied in various parts, all without departing fromthe scopeof the invention, it is to be understood that all matterhereinbefore set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense.

I claim:

1. An abrasive article comprising diamonds bonded with a hard, friable,sintered metal bond capable of being sintered at between 600 C. and 850C. and said metal bond comprising copper, iron and tin, with not lessthan 20% of the total metal being cold moldable metal selected from thegroup consisting of copper and nickel, with not less than 4% of thetotal metal being copper, with not less than 2% of the total metalhaving a high melting point'and being selected from the group consistingof iron and nickel, with not less than 1% of the total metal being iron,the total amount of tin being at least 2% in excess of the tin in; solidsolution at around bond after sintering being not lower than 750 C.

2. An abrasive article comprising diamonds bonded with a hard, friable,sintered metal bond comprising copper, iron and tin, the proportions ofeach of said metals by weight to the entire metal bond being not lessthan 25%.

20 C'., and the fusing point of the entire metal 45 3. An abrasivearticle comprising diamonds bonded with a hard, friable, sintered metalbond comprising approximately 25% iron, 25% copper, 25% tin-and 25%nickel by weight.

4. An abrasive article consisting of a steel "backing and an abrasiveportion metallurgically united thereto and comprislng' diamonds bondedwith a copper, tin, iron bond.

5. An abrasive article consisting of a steel backing and an abrasiveportion metallurgically united thereto and comprising diamonds bondedwith a copper, tin, iron, nickel bond.

6. An abrasive article comprising abrasive grains bonded with a hard,friable, sintered metal bond capable of being sintered at between 600 C.and 850 C. and said metal bond comprising copper, iron and tin, with notless than 20% of the total metal being cold moldable metal seiected.from the group consisting of copper and nickel, with not less than 4% ofthe total metal being copper, with not less than 2% of the total metalhaving a high melting point and being selected from the group consistingof iron and nickel, with not less than 1% of the total metal being iron,the total amount of tin being at least 2% in excess of the tin in solid'solution at around 20 C., and the fusing point of the entire metal bondafter sintering being notlower than 7.50 C.

'7. An abrasive article comprising abrasive grains bonded with a hard,friable, sintered metal bond comprising copper, iron and tin, theproportions of each of said metals by weight to the entire metal bondbeing not less than 25%.

8. An abrasive article comprising abrasive grains bonded with a hard,friable, sintered metal bond comprising approximately 25% iron, 25%copper, 25% tin and. 25% nickel by weight.

= EDWARD VAN nan PYL.

